Pressure Swing Processes

FIGURE 11.18. The basic two-bed pressure swing adsorption system. (After Skarsirom from ref. 32 reprinted with permission.) 

From a thermodynamic perspective the essential difference between PSA and thermal swing processes is that in the PSA system the energy recfuired to achieve the separation is put into the system as mechanical work rather than as heat. Since mechanical energy is generally more expensive than heat, efficient utilization of energy is essential for an economic PSA system. Such considerations become especially important in the larger scale units. 

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The desorption using a nonadsorbing medium such as nitrogen equals a pressure swing process because the purge gas reduces the partial pressure of the n-alkane and works as a vacuum. This variant also is only suitable for the isolation of n-alkanes from low molecular weight hydrocarbon mixtures like gasoline fractions. 

Whysall, M. and L.J.M. Wagermans, Very Large Scale Pressure Swing Processes, U.S. Patent No. 6,210,466 Bl, 2001. 

PS Claus A process for recovering sulfur from waste gases by a combination of the Pressure swing process and the Claus process. 

Dehydration by the pressure swing process is largely the province of activated alumina or silica gel type adsorbents. Owing to the nature of their isotherms they demonstrate more favorable desorption characteristics for use in PSA. 

In pressure-swing processes, it Is quite common to use a fraction of the less-adsorbed gas product as a low-pressure purge gas, as shown In Figure 2. Often the purge flow is in the opposite direction from the feed flow. Rules for the minimum fraction of less-adsorbed gas product for displacing... 

Gas Bulk Separations Recovery of oxygen and nitrogen by various pressure-swing processes will continue to grow Oxygen from these processes is already being produced for waste-treatment plants, for welding shops and for ln-home care of... 

General information on pressure-swing distillation can be found in Van Winkle (Distillation, McGraw-Hill, New York, 1967), Wankat (Ejmilibrium-Stased Separations, Elsevier, New York, 1988), and Knapp and Doherty [Ina. Eng. Chem. Res., 31, 346 (1992)]. Only a relatively small fraction of azeotropes are sufficiently pressure-sensitive for a pressure-swing process to be economical. Some applications include the minimum-boiling azeotrope tetrahydrofuran-water [Tanabe et al. ... 

Since the iC5/methanol azeotrope is pressure sensitive (79 mol% iC5 at 10 bar and 67 mol% iC5 at 4 bar), it is possible to use a pressure-swing process with two distillation columns, operating at two different pressures, to separate methanol from the C5 components. An alternative separation process for this system is extractive distillation, which is studied in this chapter. 

Pressure-swing process Alternating between elevated pressure during adsorption and pressure reduction during desorption Gas separation, e.g., Nj from air, CH4 from biogas, CH4 from hydrogen Raw gas compression lean gas stream in addition to the product gas stream... 

Most of the flow directions in a pressure-swing process are fixed relative to one another. The most common configuration is for adsorption to take place upflow, thus the name blowdown for counteicunem depressurization. Therefore, some precautions must be taken to assure that no bed lifting or crashing occurs (see below). Pressure-swing stqis are more diflicuh to assess because many steps such as depressurization, blowdown, pressurization, and equalization b in at a high flow rale and decrease to low or no flow. 

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